This invention relates generally to ovens, and more particularly to convection ovens having a fan for circulating hot air throughout the cooking chamber of the oven, and specifically to a gas heated convection oven having improved cooking characteristics and lower production of carbon monoxide.
Convection cooking ovens are well known in the art. The term convection oven is used to describe anr oven having a mearis for circulating heated air within the cooking chamber ofthe oven. Air circulation within the cooking chamber results in a more even temperature distribution within the oven. Furthermore, the improved transfer of heat into the food item resulting from the hot air circulation results in a reduction in the time required to cook food items inra convection oven when compared to a standard oven operatingat the same temperature.
Convection ovens have proven to be more effective for roasting than for baking. The term roasting is generally understood to refer to browning or parching by exposing to heat, and is generally used in connection with the cooking of heavy foods such as meat. Baking, on the other hand, is generally understood to mean drying or hardening by subjecting to heat, and is generally used in connection with cooking lighter flour-based foods such as breads, cakes, pastries and cookies. A typical temperature range for roasting may be 300-350 degrees Fahrenheit, while a typical baking temperature may be 300-400 degrees Fahrenheit.
It is know that baked goods do not react well to the speedier cooking process of a convection oven. Although even heat distribution throughout an oven is a desirable feature for all types of cooking, prior art convection ovens having even heat distributions have proven to be less than optimal for baking.
Furthermore, modem gas ovens must be designed to miriimize the production of carbon monoxide (CO) during the gas combustion process. Most current production gas-heated convection ovens can not meet a requirement for maintaining CO levels within the oven to less than 800 ppm. Electric ovens do not produce carbon monoxide, but they are not preferred in many applications because of their slower heating times and higher cost of operation.
Carbon monoxide levels in a gas oven typically spike to a very high level when the gas burner is first ignited due to the fact that all of the oven surfaces are cold. As the oven heats to its operating temperature, the CO levels-are gradually reduced to their steady state levels. It is known that the operation of the fan in a convection oven will increase the amount ofcarbon monoxide produced. Therefore, the operation of the fan is delayed in some gas oven designs until several minutes after first ignition in order to avoid a further increase in the initial CO level spike. Nonetheless, peration of a convection oven fan will result in an increase in the undesirable generation of carbon monoxide in a prior art gas convection oven.
Thus there is a need for an oven that provides the speed of cooking of a convection oven without the disadvantages of poor, baking properties. While such an oven would preferably be gas fired, there is a need to avoid the high carbon monoxide production levels normally associated with gas fired convection ovens.
Disclosed herein is an oven having a cooking chamber; a fan for circulating heated air within the cooking chamber; and a user selectable switch connected to the fan and operable to vary the speed of operation of the fan. The fan may be operable at a first speed and at a second speed faster than the first speed, and the user selectable switch may have a first position for baking wherein the fan is operated at the first speed, and a second position for roasting wherein the fan is operated at the second speed.
The oven disclosed herein may further have the fan disposed within a recess formed in a wall of the cooking chamber; and a cover plate attached to the wall and covering the fan to define a fan chamber; the cover plate further having a plurality of openings proximate a central portion of the cover plate for the passage of the heated air from the cooking chamber into the fan chamber, and three openings disposed proximate a periphery of the cover plate for the passage of heated air from the fan chamber into the cooking chamber. The three openings may each have a generally elliptical shape and may each be positioned to have an edge located adjacent an edge of the recess in order to provide a smooth flow path for the heated air passing into the cooking chamber. The three openings may be spaced equidistant around the perimeter of the cover plate, wherein a first of the three openings is centered along an imaginary line located at a forty five degree angle above horizontal.